Postnatal heart maturation is the basis of normal cardiac function and provides critical insights into heart repair and regenerative medicine. While static snapshots of the maturing heart have provided much insight into its molecular signatures, few key events during postnatal cardiomyocyte maturation have been uncovered.Here we processed bulkRNASeq and ChIPSeq of Cardiomyocyte at different postnatal time points. Overall design: RNA-Seq of mouse/rat cardiomyocytes in postnatal; ChIP-Seq of H3K4me1, H3K4me3, H3K27me3, H3K27ac and Pol II in mouse cardiomyocytes in postnatal